Source : Webster's Revised Unabridged Dictionary (1913)

Angle of incidence \Angle of incidence\ (A["e]ronautics)
   The angle between the chord of an a["e]rocurve and the
   relative direction of the undisturbed air current.

Incidence \In"ci*dence\, n. [Cf. F. incidence.]
   1. A falling on or upon; an incident; an event. [Obs.] --Bp.
      Hall.

   2. (Physics) The direction in which a body, or a ray of light
      or heat, falls on any surface.

            In equal incidences there is a considerable
            inequality of refractions.            --Sir I.
                                                  Newton.

   {Angle of incidence}, the angle which a ray of light, or the
      line of incidence of a body, falling on any surface, makes
      with a perpendicular to that surface; also formerly, the
      complement of this angle.

   {Line of incidence}, the line in the direction of which a
      surface is struck by a body, ray of light, and the like.

Source : WordNet®

angle of incidence
     n : the angle that a line makes with a line perpendicular to the
         surface at the point of incidence [syn: {incidence angle}]